Donald Trump's former campaign chairman Paul Manafort lied to the special counsel investigating Russia's interference in the 2016 U.S. presidential election, breaching his plea agreement, according to a court filing on Monday.

Manafort said in the same filing he disagreed with Special Counsel Robert Mueller's assertion that he lied to investigators.

Both the special counsel and Manafort's attorneys agreed there was no reason to delay his sentencing and asked the court to set a date for that.

Mueller, who is also probing possible collusion between Moscow and the Trump campaign, said in the filing that after signing a plea agreement: "Manafort committed federal crimes by lying to the Federal Bureau of Investigation and the Special Counsel's Office on a variety of subject matters."

Mueller said in the filing that those lies breached Manafort's plea agreement.

Manafort's attorneys said in the same filing submitted to U.S. District Judge Amy Berman Jackson in Washington that Manafort had met with the government on several occasions and provided information "in an effort to live up to his cooperation obligations."

They said Manafort disagreed with the characterization that he had breached the agreement.

The breakdown in the plea deal raises the prospect that Manafort is seeking to protect others who worked on Trump's campaign and to curry favor with the president, said former federal prosecutor David Weinstein.

"It seems to me he's angling for the pardon," he said.

Manafort, a longtime Republican political consultant who made tens of millions of dollars working for pro-Kremlin politicians in Ukraine, ran the Trump campaign as it took off in mid-2016.

He attended a meeting at Trump Tower in June 2016 with a group of Russians offering damaging information on Democratic candidate Hillary Clinton, who lost in an upset to Trump in the presidential vote that November.

Russia denies U.S. allegations it hacked Democratic Party emails and ran a disinformation campaign, largely on social media. Trump denies any campaign collusion and calls the investigation a political witch hunt.

Manafort had started cooperating with Mueller's prosecutors in September this year after pleading guilty to conspiracy against the United States - a charge that including a range of conduct from money laundering to unregistered lobbying, and to attempting to tamper with witnesses.

The deal required him to cooperate completely with the government, including testifying before any grand juries or at any trials. In return, Mueller promised to argue for leniency at sentencing.

The agreement pertains to one of two cases against Manafort. He was convicted by a jury in August on tax and bank fraud charges in the other case in Virginia.

Rudy Giuliani, who represents Trump in the Russia investigation, told Reuters in October that he had periodically spoken with Manafort's lawyer, Kevin Downing, and that he believed Manafort had not provided any information to prosecutors that was damaging to the president.